Tropical Storm DELTA

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TROPICAL STORM DELTA DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
4 AM EST FRI NOV 25 2005
 
INFRARED SATELLITE IMAGERY THIS MORNING SHOWS THAT DELTA HAS BECOME
LESS ORGANIZED DURING THE PAST 6 HR...WITH THE MAIN CONVECTION
CURRENTLY CONFINED TO RAGGED BANDS OVER THE EASTERN SEMICIRCLE.  THE
CIRRUS OUTFLOW IS FAIR OVER THE EASTERN SEMICIRCLE AND NON-EXISTENT
ELSEWHERE.  SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND
SAB...AND 35 KT FROM AFWA.  BASED ON THIS...THE INITIAL INTENSITY
IS REDUCED TO 55 KT.

THE INITIAL MOTION IS 220/3...BASED ON A 6 HR MOTION.  AT THIS
TIME...DELTA IS IN WEAK STEERING CURRENTS EAST OF A WEAKENING
DEEP-LAYER RIDGE OVER THE MID-ATLANTIC.  THIS SHOULD RESULT IN
ERRATIC MOTION...AND LITTLE OVERALL MOTION IS EXPECTED TODAY. 
AFTER 24 HR...FALLING PRESSURES WEST OF DELTA ASSOCIATED WITH AN
APPROACHING SHORTWAVE TROUGH AND DEVELOPING SURFACE LOW SHOULD MOVE
THE STORM NORTH-NORTHEASTWARD OR NORTHWARD.  THE VARIOUS TRACK
GUIDANCE MODELS AGREE ON THIS THROUGH 48 HR...THEN ARE EVEN MORE
AGGRESSIVE IN TURNING DELTA EASTWARD IN WESTERLY FLOW SOUTH OF A
DEVELOPING TROUGH OVER WESTERN EUROPE THAN THEY WERE 6 HR AGO. 
WHILE THE MODELS AGREE WELL ON THE EASTWARD MOTION...THIS WAS NOT
THE CASE 12 HR AGO...AND IT WILL TAKE A RUN OR TWO MORE SHOWING
THIS MOTION BEFORE THE FORECAST TRACK CAN FULLY FOLLOW IT.  THE NEW
FORECAST TRACK IS SHIFTED EAST OF THE PREVIOUS TRACK AFTER 24 HR...
AND SIGNIFICANTLY CHANGED TO A MORE EASTWARD MOTION AFTER 72 HR. 
HOWEVER...THE TRACK IS ALONG THE NORTH SIDE OF THE GUIDANCE
ENVELOPE AND IS SLOWER THAN ALL THE MODELS SAVE THE UKMET.  IF
SUBSEQUENT MODEL RUNS CONTINUE FORECASTING A FASTER EASTWARD
MOTION...AND IT CONTINUES TO APPEAR THAT DELTA WILL NOT BE ABSORBED
INTO THE NEW LOW TO THE WEST...ADDITIONAL REVISIONS TO THE TRACK
FORECAST MAY BE NECESSARY IN LATER ADVISORIES.
 
THE TREND OF DECREASING ORGANIZATION REDUCES THE CHANCE THAT DELTA
WILL BECOME A HURRICANE.  THE LARGE-SCALE MODELS AND THE SHIPS
MODEL FORECAST VERTICAL SHEAR TO INCREASE AS THE UPPER-LEVEL
CYCLONIC SHEAR AXIS CURRENTLY NEAR THE STORM WEAKENS AND MOVES
EASTWARD...AND THIS MAY ALREADY BE UNDERWAY.  THE INTENSITY
FORECAST IS THUS CHANGED TO SLOW WEAKENING DURING THE NEXT 48 HR AS
DELTA MOVES NORTH-NORTHEASTWARD...FOLLOWED BY EXTRATROPICAL
TRANSITION AS THE STORM TURNS EASTWARD SOUTH OF THE EUROPEAN
TROUGH.  IF THE SHEAR INCREASES AS MUCH AS THE MODELS ARE
SUGGESTING...DELTA COULD WEAKEN FASTER THAN CURRENTLY FORECAST.
 
FORECASTER BEVEN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/0900Z 23.7N  39.3W    55 KT
 12HR VT     25/1800Z 23.6N  39.4W    55 KT
 24HR VT     26/0600Z 24.0N  39.0W    55 KT
 36HR VT     26/1800Z 25.0N  38.3W    50 KT
 48HR VT     27/0600Z 26.8N  37.1W    50 KT
 72HR VT     28/0600Z 31.0N  34.0W    45 KT...BECOMING EXTRATROPICAL
 96HR VT     29/0600Z 32.0N  28.0W    45 KT...EXTRATROPICAL
120HR VT     30/0600Z 32.0N  21.0W    45 KT...EXTRATROPICAL
 
 
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